Self-Affine Sets and Graph-Directed Systems

   Abstract. A self-affine set in R ⁿ is a compact set T with A(T)= ∪ _{d∈ D} (T+d) where A is an expanding n× n matrix with integer entries and D ={d ₁ , d ₂ ,···, d _N } ⊂ Z ⁿ is an N -digit set. For the case N = | det(A)| the set T has been studied in great detail in the context of self-affine tiles. Our main interest in this paper is to consider the case N > | det(A)| , but the theorems and proofs apply to all the N . The self-affine sets arise naturally in fractal geometry and, moreover, they are the support of the scaling functions in wavelet theory. The main difficulty in studying such sets is that the pieces T+d, d∈ D, overlap and it is harder to trace the iteration. For this we construct a new graph-directed system to determine whether such a set T will have a nonvoid interior, and to use the system to calculate the dimension of T or its boundary (if T ^o ≠  ). By using this setup we also show that the Lebesgue measure of such T is a rational number, in contrast to the case where, for a self-affine tile, it is an integer.     

Measure of Self-Affine Sets and Associated Densities

Let \(B\) be an \(n\times n\) real expanding matrix and \(\mathcal {D}\) be a finite subset of \(\mathbb {R}^n\) with \(0\in \mathcal {D}\) . The self-affine set \(K=K(B,\mathcal {D})\) is the unique compact set satisfying the set-valued equation \(BK=\bigcup _{d\in \mathcal {D}}(K+d)\) . In the case where \(\#\mathcal D=|\det B|,\) we relate the Lebesgue measure of \(K(B,\mathcal {D})\) to the upper Beurling density of the associated measure \(\mu =\lim _{s\rightarrow \infty }\sum _{\ell _0, \ldots ,\ell _{s-1}\in \mathcal {D}}\delta _{\ell _0+B\ell _1+\cdots +B^{s-1}\ell _{s-1}}.\) If, on the other hand, \(\#\mathcal D<|\det B|\) and \(B\) is a similarity matrix, we relate the Hausdorff measure \(\mathcal {H}^s(K)\) , where \(s\) is the similarity dimension of \(K\) , to a corresponding notion of upper density for the measure \(\mu \) .     

On Lebesgue Measure of Integral Self-Affine Sets

Let A be an expanding integer n×n matrix and D be a finite subset of ? ⁿ . The self-affine set T=T(A,D) is the unique compact set satisfying the equality \(A(T)=\bigcup_{d\in D}(T+d)\). We present an effective algorithm to compute the Lebesgue measure of the self-affine set T, the measure of the intersection T∩(T+u) for u∈? ⁿ , and the measure of the intersection of self-affine sets T(A,D ₁)∩T(A,D ₂) for different sets D ₁, D ₂?? ⁿ .     

Construction of Wavelet Sets Using Integral Self-Affine Multi-tiles

Gabardo and Yu first considered using integral self-affine tiles in the Fourier domain to construct wavelet sets and they produced a class of compact wavelet sets with certain self-similarity properties. In this paper, we generalize their results to the integral self-affine multi-tiles setting. We characterize some analytic properties of integral self-affine multi-tiles under certain conditions. We also consider the problem of constructing (multi)wavelet sets using integral self-affine multi-tiles.     

L-偏序集上的闭包系统

给出L-幂集上LK-闭包系统的等价刻画。提出L-偏序集上闭包系统的概念并讨论其基本性质。最后,将经典偏序集和L-幂集上关于闭包算子和闭包系统的对应理论推广到L-偏序集上。     

二值命题逻辑中的极大命题集与完备命题集

系统讨论了二值命题逻辑系统中极大命题集与完备命题集,给出了两种命题集的等价描述和表示定理,揭示了极大命题集和完备命题集的深刻内涵和联系.     

Combining Perfect Systems of Difference Sets

We use sharply 2-transitive permutation groups to constructan additive sequence of permutations from a system of differencesets, each component of which has size one less than a primepower. This allows us to combine perfect systems of differencesets to form other perfect systems. In particular, if thereexists a perfect (m, n + 1, 1)-system and a perfect (q, n +1, 1)-system then there exists a perfect (mqn(n + 1) + m + q,n + 1, 1)-system.     

传递系统中的不变攀援集

推广了攀援集的概念.研究了传递系统中的不变攀援集.证明了在相当广泛的条件下,一个传递系统有一个不变的稠密的σ-Cantor子集是完全攀援集.     

关于粗糙集和灰色系统之间某些关系的探讨

首先介绍粗糙集与灰色系统两种理论,并对二者进行比较。接着介绍普通粗糙集、P-粗糙集以及灰色集的定义,并就灰色集、模糊集和经典集合三者进行对比分析。我们提出了点灰度和集灰度两种灰度概念用于描述灰色系统的信息不确定性。通过P粗糙集导出相应的灰色集,并研究相关的灰度、粗糙度与边界域的性质和关系。分析表明使用导出的灰色集对系统的信息不确定性的估计与相应的粗糙集是一致的,因此两种理论在描述和处理不确定性信息系统方面的一定的相关性,将两种理论相结合来处理某些不确定性信息系统可能更为有效。     

Rigidity Theorem for Self-Affine Arcs

Doklady Mathematics - It has been known for more than a decade that, if a self-similar arc $$gamma $$ can be shifted along itself by similarity maps that are arbitrarily close to identity, then...     

Self-Affine Fractal Functions and Wavelet Series

We consider functions represented by series ∑_g  G c_gψ(g ^− 1(x)) of wavelet-type, where G is a group generated by affine functions L₁,…,L_n and ψ is piecewise affine. By means of those functions we characterize the class of self-affine fractal functions, previously studied by Barnsley et al. We compute their global and local Hölder exponents and investigate points of non-differentiability. Wavelet-representations for various continuous nowhere differentiable and singular functions are presented. Another application is the construction of functions with prescribed local Hölder exponents at each point.     

广义信息系统上的Rough集理论

给出了广义信息系统以及其上的广义关系,在统一的模型下研究了知识约简问题.通过属性集上的闭算子给出了简化约简的方法.     

集合关于脉冲微分系统的稳定性

利用分段连续的李雅普诺夫函数及比较原理,通过建立比较原理,把集合对脉冲微分系统稳定性的判定化成集合对脉冲微分方程稳定性的判定.     

Fuzzy信息系统的Rough集理论

提出 Fuzzy信息系统的概念 ,建立 fuzzy信息系统上的 Rough集理论 ,给出 Fuzzy信息系统与经典信息系统的关系 ,讨论 Fuzzy信息系统的知识约简问题     

Localization of Invariant Sets of Dynamical Systems

Invariant sets of dynamical systems are considered. The localization inside some compact set and isolating neighborhoods are constructed. Bibliography: 6 titles. Illustrations: 3 figures.